This invention relates generally to maintenance and repair of sewer system manholes. More particularly, the invention relates to an improved method of lining or relining manholes to reinforce, seal and rehabilitate them.
In todays' efforts to clean up our environment and minimize pollution, it has been mandated by the Environmental Protection Agency that cities must stop the flow of sewage into streams, lakes, rivers and oceans. The overloading of modern sewage systems is caused by several factors, including the growth of our cities, and the inevitable aging of sewer systems, and the poor quality associated with installation of new systems. The deterioration of associated manholes is a major cause for alarm.
Complex sewer utilities comprises a variety of interconnected lines, pumping stations, conduits and the like. Municipal sewers typically comprise a plurality of networked, generally horizontally extending underground lines which are generally, but not always, built adjacent to and beneath the street network. These sewers include horizontal, subterranean lines formed of longitudinally aligned sections of slightly inclined pipes, which terminate periodically within manholes. A manhole is essentially a vertical passageway, typically beginning at ground level or at the street surface, which extends into the ground and receives one or more sewer line junctions. Manholes enable human access to line junctions and installations, for system inspections, maintenance and repairs.
Typical manholes are formed of bricks, tiles or concrete blocks bonded together with cement mortar, built via a plurality of construction techniques. Pre-cast and "cast in place" concrete manholes are also common. The chimney structure may be of uniform diameter at the manhole top, but usually the structure diverges downwardly towards a non-uniform lower volume adjacent to the sewer invert. The sewer pipes connect at the bottom of the manhole entryway through an exposed, open-air invert which permits human access to the sewer pipeline system.
As will be readily appreciated by those skilled in the art, numerous problems are experienced by sewer systems as time goes on. For example, joints eventually leak, and pipe lines may become broken or discontinuous. In addition, debris may collect and jam the system, and tree roots, which are drawn to the nutrient rich sewer lines, will eventually cause cracking and interrupting sections of the system. Many of the issues involved in sewer maintenance and repair are discussed in detail in a publication entitled Utility Infrastructure Rehabilitation, published by the United States Department of Housing and Urban Development, Office of Policy Development and Research, Building Technology Division, November 1984, which is hereby incorporated by reference.
While it will be recognized that numerous problems can occur to the sewer pipelines themselves, other urgent problems primarily relating to water seepage and leaking, infect conventional manhole structures. Overloading from inflow and infiltration caused by rains is serious. Run-off goes directly into typical manholes. This inflow and infiltration causes flooding of the system and overloading of "downstream" treatment plants, and as a result raw sewage can be discharged directly into the environment by way of the drainage system, much of which is above ground. Such inflow and infiltration will increase the flow in the system as much as ten times in some instances and an increase of three to four times is not uncommon. Studies have shown that as much as 75% of the inflow during rainy periods is through the manholes and the remaining 25% is through the transport lines between each manhole. Of course exfiltration is dangerous as well.
Many of our sewage systems are fifty years old or older. All of the older systems were built with brick or block with mortared joints. With the deteriorations of the bricks and mortar, many of these old manholes have partially or completely collapsed, and they allow ground water to pass freely into the gathering system. Older manholes which are not on the verge of outright structural collapse usually leak severely, and thus contribute significantly to water infiltration and downline system overflow. As the brick, concrete, concrete block and mortar combination tends to decay, the entire system may practically fall apart. Ground water can leak around and through the loose bricks, tiles, blocks, concrete or mortar and penetrate the manhole, dropping onto the invert and entering the sewer system. Surface water or drainage can occur around the manhole ring. Concrete manholes allow infiltration and/or exfiltration as a result of honeycombing, cold joints, or improperly sealed joints.
Thus ground water and flash flood or surface water, for example, typically can enter a sewer system through and around leaks in the manhole structure, quickly overfilling the lines. This flood water will quickly overpower the system, and cumulative over-pressure transmitted to a downline manhole may result in a vertically upwardly movement of water which will deflect the manhole cover and scatter untreated sewage directly upon the streets above.
This excess water, which would not require municipal treatment but for its entry into the sewer system, flows to the treatment facility resulting in unnecessary treatment cost. Also, the excess exceeds the design capacity of the typical treatment plant, resulting in inadequately treated sewage, and the discharge of offensive effluent into streams, lakes, rivers and oceans.
A reliable and cost-efficient system to restore and maintain manhole structural integrity for stopping the inflow and/or infiltration/exfiltration of water through the sewer system, or raw sewage out of the system, is thus necessary.
While it has long been appreciated that periodic maintenance and rehabilitation activities must be conducted for proper sewer utility administration, the necessity of proper manhole maintenance has not been emphasized. In the prior art it is known to patch leaks in manhole brick, concrete block and concrete structures through the application of chemical grouting. Grouting is a method often used to seal leaking joints and circumferential cracks in non-pressure pipelines, such as sewer pipes. The principal chemical grouts currently available are acrylamide gel, acrylate gel, urethane gel and polyurethane foam. Foam grouts form an in place pipeline type of gasket and can cure to a tough flexible and cellular, rubber-like material. A seal is created within the joint with minimum penetration of the material to the outside of the joint or pipeline. Gel grouts, on the other hand, penetrate to the outside of the joint and pipeline, both filling the joint and forming an external seal as it mingles with the soil and fills voids outside the joint. The grout and soil mixture cures to a relatively impermeable and somewhat flexible collar within and on the outside of the joint.
The most commonly used gel grouts are acrylamide gel, acrylate polymer and urethane gel. All are resistant to the chemicals found in sewer lines. Foam grouts are liquid urethane prepolymers which are catalyzed by water during injection. Immediately upon injection, the foaming reaction of the grout and water, together with the injection pressure, expands the material into the joint cavity. Foam grouts, sometimes called elastomeric grouts, are difficult to apply. Chemical grouts are also used, but they have no structural properties capable of insuring an effective seal where joint or circumferential cracking problems are due to on-going settlement or shifting of the pipeline. Additionally, there are concerns about the effects of these products on our environment.
As recited in the aforementioned publication, Utility Infrastructure Rehabilitation, pages 5-57 through 5-58, there exists three common methods which are used for rehabilitating manhole structures. It is known to apply coating to the interior wall of the manhole, and coatings can be made of epoxy, acrylics, polyurethanes etc. They may be applied directly over brick, tile, concrete block or concrete and to a certain extent they are waterproof and corrosion resistant. Typically an epoxy coating is applied by troweling. Acrylic coatings are applied with a brush and polyurethane coatings have been applied with an airless sprayer. For repairs, the surface of the manhole must be clean and free of debris. Generally a structurally sound manhole is required and rinsing and cleaning through detergents and various forms of cleaning solutions may be necessary. Proper surface cleaning is critical, and the surface must be allowed to properly dry for certain types of coatings such as polyurethane. In general all leaks must be plugged using patching or grouting materials. Usually quick drying grouts are used and they are troweled into place. It is known to employ cement patches, polyurethane foam and a variety of chemical grouting materials to stop leaks.
Chemical grout may also be applied about the buried exterior of manholes. Large volumes may be pumped into the usually irregular and unpredictable void between the outside of the manhole and the surrounding ground. A non-homogeneous irregular and inconsistent mixture which results is incapable of "sealing" a manhole even after curing of the chemical material. This method may be used to reduce infiltration through cracks and holes, but an economically excessive volume of grout is usually needed in these circumstances. Since its volume cannot adequately be determined prior to application, its use is unfavored.
Finally it is also known to insert a structural liner inside an existing manhole. The liner must conform to the configuration of existing manhole as closely as possible, and it must usually be custom designed and made. Other means of rehabilitating include the use of a sleeve or cylinder disposed within the manhole which forms an annulus between itself and the existing brick structure. The annulus is filled with grout to form a lining. However, since the confines of the manhole are extremely irregular, the temporary liner is difficult to properly configure, and the operation is haphazard and unreliable at best.
Mortar, generally a mixture of lime, cement or both with sand and water is used as a bonding agent between brick, tile or concrete blocks. Grout is a form of mortar used to fill narrow cavities such as joints, rock fissures, gaps between adjacent bricks, tile, concrete blocks or rocks. Shotcrete is often referred to as mortar or concrete conveyed through a hose and pneumatically projected at a high velocity onto a surface. This is also referred to as "gunned" concrete or gunnite. Information on shotcrete is seen in ACI Standard Recommended Practice for Shotcreting (ACI 506-66) published 1966 by the American Concrete Institute. In the wet mix process "shotcreting" all of the ingredients including the mixing water are first thoroughly blended and the mortar or concrete mixture is introduced into the chamber of the delivery equipment. Compressed air is employed to thrust the mixture through a hose and delivery apparatus and the mixture is jettisoned from the nozzle at high velocity onto a surface to be "shotcreted."
A variety of prior art mortars have been developed for shotcreting. Shotcreting is advantageous because it is often more economical than conventional concrete. It requires only a small portable plant for manufacture and placement. It can produce an excellent bond with a number of materials and it is ideal for roofing, certain coatings over brick and masonry, the encasement of structural steel for fireproofing, and the repair of deteriorated concrete structures. However, while the durability of shotcrete structures has been generally good, shotcrete repair work is subject to severe frost action and aggressive water action. In other words, known shotcrete coatings are easily degraded by exposure to water, particularly pressurized water. As a result, it is known to apply hot linseed oil to shotcrete to enhance its water resistance characteristics.
The shotcrete may include either Portland cement or calcium aluminate cement which is a rapid hardening cement. Sand, properly graded, is employed for aggregate. Other light weight aggregates may be used. Various admixtures such as accelerators like calcium chloride, air-entraining admixtures, retarders, and mineral admixtures are known. It is known to employ fly ash for increasing plasticity, reducing sagging and improving resistance to sewer gases such as sulfates. Asbestos fibers, clay and other materials have also been known to serve these purposes. Typically known mineral admixtures result in shrinkage and a decrease in strength and durability of the finished product. Also, shotcrete is typically very sensitive to the surface characteristics of the target. For example, it has generally been found unsatisfactory for the wet and moist conditions encountered in sewers. Rebound and nozzle forces caused by the necessary high volume of compressed air and sand make the process difficult and unworkable. Further, a recommended minimum thickness of two inches of material applied over a welded wire reinforcing mesh is typical. This system is labor intensive, time consuming, and expensive. Crew experience is critical in shotcreting applications. Thus shotcreting is not a viable method for manhole rehabilitation.
An American Concrete Institute (ACI) publication entitled Concrete Sanitary Engineering Structures, ACI-350R-77, published 1977, discusses a variety of considerations and special requirements for using concrete mixtures on sanitary engineering structures. The publication discusses the use of certain materials upon reservoirs and manholes and recognizes that wide cracks and other structural damage accumulating over the years promotes leakage. In order to promote "water tightness" the concrete must be impervious to liquids, crack width must be minimized, and the joints must be properly sealed. It is recognized in the art to provide minimum permeability by using water-cement ratios as low as possible consistent with workability, and that subsequent surface treatment by troweling or the use of smooth forms give good results.
The prior art reflects numerous patents which teach the relining or repair of sewer conduits with add-on, sleeve-like liners. U.S. Pat. No. 4,796,669 Issued to St. Onge, Jan. 10, 1989 discloses a method for relining buried pipeline by coaxially inserting interconnected plastic sections of tubing within the pipeline. These sections are glued together until the entire pipeline has been relined. U.S. Pat. No. 4,245,970 issued, issued Jan. 20, 1981 also discloses the relining of a sewer pipe with plastic pipe liner. Britain patent No. 4,818,314 issued Apr. 4, 1989 discloses a similar system including a plurality of liner segments for relining pipelines. U.S. Pat. No. 4,846,147 issued July 11, 1989 discloses a chimney liner system wherein a sleeve formed from a fiberglass cloth is inserted interiorly to reline the chimney.
U.S. Pat. No. 4,456,401 issued June 26, 1984 employs a felt liner impregnated with a liquid resin material inserted within the sewer line for repair. U.S. Pat. No. 4,386,628 Issued June 7, 1983 teaches the maintenance lining passageways by inserting into it a flexible tubular material of a lower diameter. The tubular material is a laminate having an outer contiguous layer of a composition foamable to form an expanded cellular structure. The pipe is expanded and solidifies in place within the pipe.
Another popular method is to provide a segmented series of pipes or liner sections inserted into the pipe to be repaired. An annulus results between the pipe and the "liner", and grout or cementitious material may be pumped into the annulus to form an interior lining. U.S. Pat. No. 4,751,799 issued June 21, 1988 employs liners comprising a plurality of individual liner sections to define the inner surface of the manhole member to be "relined". The resultant annulus thereafter receives grout. U.S. Pat. Nos. 4,728,223, issued Mar. 1, 1988; 4,602,659 Issued to Parkyn July 29, 1986, Parkyn 4,601,312 issued July 22, 1986, and 4,350,548 issued Sept. 21, 1982 all depict systems in which a resultant annulus is filled with grout.
U.S. Pat. No. 4,325,772 issued Apr. 20, 1982, shows the use of flexible liner tube within an installed pipe, and a liquid adhesive agent is forced into the annulus formed there between. Allen Pat. No. 4,678,370 issued July 7, 1987 discloses a system of helically wound internal liners which define an annulus within the sewer pipe for receiving cementitious grout. A related invention is seen in Telford patent No. 3,269,421 issued Aug. 30, 1966. U.S. Pat. No. 3,834,433 issued to Larson on Sept. 10, 1974 discloses a sewer repair apparatus adapted to be moved within a pipe and centered upon a leaking area. Ends of the apparatus thereafter expand to form a seal, centered over the leaking pipe area. Subsequent pressurization of this area forces grout outwardly through the annulus, through the ends of the pipe, and forms an internal and external coverage for patching the leak.
A number of patents also relate to the mechanical concept of providing a mechanically moving carriage which travels through the pipe and services it on the way. These devices are limited to pipes running horizontally or near a horizontal plane and of a constant diameter. Lona U.S. Pat. No. 4,777,905, issued Oct. 18, 1988 is typical. A carriage is guided coaxially through a pipeline to be repaired, and it applies a coating through a plurality of radially operated rollers which contact the underside of the pipe wall. Similarly, Cook U.S. Pat. No. 2,894,539 issued July 14, 1959 discloses apparatus for traveling through the interior of the pipeline which concurrently applies sealant. U.S. Pat. Nos. 4,181,484, issued Jan. l, 1980 and U.S. Pat. No. 4,781,556 show similar techniques.
Crom U.S. Pat. No. 2,484,018 issued Oct. 11, 1949 discloses a carriage mounted system which moves axially through a horizontal grout radially through a spraying process. Nakashin U.S Pat. No. 4,370,113 also discloses a carriage movable axially within a pipe which applies grout radially within the pipe. Also relevant is U.S. Pat. No. 3,728,223 which constructs an internal reliner through apparatus moving through the center of the pipeline.
U.S. Pat. No. 4,769,077 issued Sept. 6, 1988 discloses a cementitious grout formulation characterized by fast setting for use and repairing concrete surfaces. Another suitable concrete is seen in U.S. Pat. Nos. 4,772,327 issued Sept. 20, 1988. U.S. Pat. No. 3,871,583 issued Mar. 18, 1975 discloses a cement spray gun with remote air injection suitable for use with spray crete. U.S. Pat. No. 4,796,814 issued Jan. 10, 1989 discloses a cement nozzle suitable for use in applying spray crete. Another spray gun is seen in U.S. Pat. No. 3,708,124, issued Jan. 2, 1973.
No known systems reveal a spray-applied, monolithic concrete liner/reliner for manholes.